Not applicable.
Not applicable.
1. Technical Field
This invention relates in general to a torque transfer module system and, more particularly, to a torque transfer module to transfer the torque between the front and rear axles or the left and right wheels of the same axle on all wheel drive vehicles or a vehicle having four wheel drive on demand.
The primary benefit of an all wheel drive vehicle is its ability to transfer engine torque to all of the wheels of the vehicle. This torque transfer allows the vehicle to retain mobility on surfaces where one or more wheels of the vehicle are unable to obtain traction. Various torque transfer devices are currently used to provide dynamic control to vehicles. Torque transfer is usually accomplished through use of a torque transfer module installed in the drive train of the vehicle. In some installations, the torque transfer module transfers torque from one axle to another axle on the vehicle. On other installations, the torque transfer module transfers torque between two wheels mounted onto a single axle of the vehicle. When one of the axles on the vehicle, or one of the wheels on a single axle, is unable to obtain traction, the torque transfer module shifts the torque from the slipping axle or wheel to the axle or wheel having better traction. Torque transfer between the wheels of the same axle can also be accomplished by using a conventional limited slip differential.
2. Description of Related Art
Early all wheel drive vehicles used a simple gear box arrangement wherein a locking device was used to mechanically connect one wheel of an axle to the other wheel. Through this mechanical locking connection, the same torque was transferred to both wheels regardless of whether either one of the two wheels was losing traction.
More recently, torque transfer systems have been invented to detect when one axle or one wheel is losing traction. The torque transfer systems then transfer torque from the slipping axle or wheel, to the axle or wheel with better traction. Several methods have been used to detect wheel slippage. The most commonly used systems utilize the signals generated from an antilock braking system installed onboard the vehicle.
U.S. Pat. No. 6,098,770 teaches a clutch assembly having a reaction force circuit which operates to control the amount of torque applied to each wheel. An internal clutch mechanism is engaged when an electrical solenoid is used to slow the rotation of a ramped plate (or circular element) in relation to another ramped plate (circular element) connected to the output shaft. The mechanical transfer of the torque is accomplished by a series of load bearing balls that ride up circular recess of one circular element, to press against a circular recess in another circular element causing the other element to engage the clutch plates in the clutch.
U.S. Pat. Nos. 5,469,950 and 5,979,631 describe another torque transmission device wherein the speed differential between two rotating shafts operates a hydraulic pump arrangement. The hydraulic pump pressurizes a clutch piston which drives an element against the internal clutch plates, thereby engaging the clutch. Cam followers are used to operate the hydraulic pump arrangement and to indicate a torque differential within the device. While the cam followers succeed in operating the hydraulic pump, the cam followers cause fluctuations in the hydraulic pump allowing pressure differentials in the compression of the clutch plates. These pressure differentials can result in increased wear in the clutch plate assembly.
The present invention offers a more compact design for a torque transfer system, optimized from the standpoint of axial length, number of components, efficiency, wear and deflections.
The present invention resides in a torque transfer module having an ability to vary the amount of torque transferred between a first rotating shaft member and a second rotating shaft member. Specifically, a clutch assembly positioned between a first rotating shaft member and a second rotating shaft member is partially or wholly engaged dependent upon the amount of electrical current applied to an electromagnetic braking/clutch mechanism such as a hysteresis or eddy current brake. The braking mechanism initiates a drag upon a ramped plate on the first rotating shaft member and forces it to apply pressure onto a ramped surface of a clutch pressure plate. The pressure placed upon the clutch pressure plate compresses the clutch discs of a clutch assembly to transfer the torque between the first rotating shaft member and the second rotating shaft member. The design of the pole structure of the electromagnetic brake/clutch is essential for the operation of the torque transfer module in a vehicle stand-still situation. When the electromagnetic clutch is energized, enough torque has to be generated in order to create a limited relative rotation between the ramped surfaces, resulting in compressing the clutch discs and causing torque transfer.